Advanced Fuel Cells May PowerMedical Implants

The Brown University fuel cells do not
require an ion-conducting membrane or selective catalysts at the electrodes to separate the fuel-containing fluids.

Fuel cells have become a hot topic because of their potential for replacing combustion engines in cars and batteries in portable electronics. Simply designed, fuel cells are more efficient at converting chemical energy into work than a heat engine. Now, researchers at Brown University have produced two microfluidic fuel cells that could power longer-running implanted devices, such as blood glucose monitors.
A typical fuel cell consists of two electrodes that are immersed in fuel-containing fluids separated by an ion-conducting membrane. The cell produces power as electrons are removed from the fuel and transported via an external circuit to be combined with positive ions crossing the ion-conducting membrane and oxygen. Conventional fuel cells have generally used either hydrogen gas or liquid methanol. More recently, prototype fuel cells have been developed to use such fuels as glucose or formate.

According to Tayhas Palmore, PhD, associate professor of engineering, biology, and medicine and lead scientist in the project, the new fuel cells “present a new paradigm toward the development and manufacture of small fuel cells for medical implants.” She adds, “There is a lot of basic science yet to be worked out. But if successful, this design could help rid a diabetic of the need to monitor blood glucose after each meal, and that would make for a significant advance in the treatment of diabetes.”

Unlike conventional configurations, the Brown fuel cells do not require an ion-conducting membrane or selective catalysts at the electrodes to separate the fuel-containing fluids. This has been a significant hurdle in designing miniature fuel cells, according to the researchers.

They explain that the new fuel cells exploit the fact that fluids do not mix under certain conditions. Palmore adds, “We take advantage of how fuels flow in small channels in that they don't mix, which means we can keep fuels separated without a membrane.”

The researcher adds that the fuel cells work in tandem to provide power under pulsating conditions that mimic the flow of blood in the body. Previous fuel cell designs had not been capable of producing a membraneless device that did not short-circuit under pulsed flow.

One of the microfluidic fuel cell designs features a branched channel that encloses six electrodes. Palmore says this fuel cell configuration is “most suitable for generating electrical power under conditions of pulsed flow.” The scientist adds that, “The design of the device makes possible the delivery of power to a chip as a result of changes in the concentration of a fuel, such as glucose. This power feedback is a necessary component in an imbedded sensor for diabetes.”